u1300L chassis and modifications

Our U1300L is a 435-series chassis.  It was used as a transport truck by the German Army (Bundeswehr.)  It has many great improvements over the old 404 and 406/416 chassis.  Here she is, right off the docks in Baltimore...

That seems like an eternity ago!  So much has been done since that day.

Having lived with two 404s and a 406, I can sum up my observations...

If the 435 (and similar) series Unimogs have a weakness, I'd say it lies in the pneumatics.  The transmission's planetary low range (gears 1-4) is air-shifted, the parking brake is pneumatic with the brakes being air over hydraulic, and all 4x4 and differential lock control is pneumatic.  A damaged or failing compressor or broken air line could be somewhat problematic if occurring in the middle of nowhere.  There are very large bundles of plastic air lines going to and fro, and things like welding slag can wreak havoc if introduced into those bundles!  (Don't ask me how I know...)  I always carry plenty of extra air line and push-to-connect splices and fittings, in both the camper and the firetruck. 

Those of you with Unimogs know that maintenance can be a nightmare.  (Oh, the dreaded sound of a simple clutch release bearing about to give up in a 404, for example.)  The photos below depict the ease of access to the U1300L chassis.  Simply remove the air intake hose, unclip a couple of heater hose lines from their holder, remove four bolts, set the front hinges et voila...

Here are a couple of shots of the air system.  This Unimog carries air in the two tanks in the left photo.  Air is stored at 18.5 bar, or over 270 psi!  It is then regulated to around 8.5 bar for all actual consumers in the chassis.  The photo on the right shows the Bosch desiccant air dryer.  The spin-on filter contains the desiccant, and is replaced regularly.  I routinely attempt to drain my air tanks, but have NEVER seen any moisture come from them.  

Our chassis is mostly stock, but there are a few important modifications worth noting.  The engine has been updated from the OM352 direct-injection naturally aspirated diesel (130 HP) to a freshly rebuilt  OM352A turbodiesel (est. 160 - 170 HP.) Also, I modified the positive drivetrain pressurization system (for deep water fording) to function manually when called for, instead of automatically with use of 4WD.  Finally, new air seats were installed in the cab.

ENGINE

Here's the rebuilt OM352A and new Schweitzer turbo...

This setup works very well, and could only be improved with the addition of an aneroid to prevent over-injection of diesel before the turbo spools up to make boost.  Without the aneroid, or fuel enrichment valve, there is some black smoke on acceleration when in pre-boost.  The turbo pumps out a maximum of about 0.8 bar, or 12 psi, and lets this seven-ton Unimog carry her camper over 10,000-foot mountain passes in top gear.  Exhaust gas temperatures run around 650 ºF cruising at 55 MPH on the Interstate, and peaked at just under 1250ºF after climbing to the top of Cameron Pass in Colorado, at 10,276 feet in elevation.  

DRIVETRAIN PRESSURIZATION DEFEAT

I modified the drivetrain pressurization system because I fear blown drivetrain seals.  In stock form, whenever 4WD is selected, the same air pressure which shifts the transmission into 4x4 also actuates a pilot valve and supplies a 1.5 bar regulator.  The pilot valve closes off the atmospheric vents from the axles, torque tubes, and transmission while the regulator pumps in 1.5 bar of air pressure.   This pressure "positively pressurizes" the entire drivetrain, preventing moisture from leaking into the components when fording deep water.

I feel that this is slight overkill for most situations, and living in Wyoming we seldom have water to ford!  Most of our 4WD work is on rocks and steep gravel, and also in mud and snow.  Should the system be engaged while the regulator was failing, too much pressure would be introduced into an UN-vented drivetrain, surely finding the weakest seal and swiftly wrecking it.  (Again, don't ask me how I know...)

The modification is quite simple in theory and implementation...  The supply line to the 1.5 bar pressurization regulator (and pilot valve) must be cut and a valve installed in it.  This valve simply prevents 4WD air pressure from enabling the drivetrain pressurization system.  Since I wanted to be able to select this option from inside the cab, I used an Ingersol-Rand 24V solenoid actuated 1/4" body-ported three way air valve.  The simple way of saying that is 4HN47 at your local Grainger store.  

It's easy to plumb this 1/4" solenoid valve into the metric air system by using 1/4" MIP to 1/4" hose barb fittings screwed into each side of the valve.  The 8mm O.D. plastic air lines used in the 435 chassis will push over a 1/4" hose barb if coaxed slightly with a heat gun.  They WILL NOT pull off, but have to be cut - just like the rest of the fittings on the Unimog.  No clamp is needed.

Here's a "Before" and "After" shot (from our U1300L firetruck)...

For the record, I also added a mechanical pressure gauge in my Overhead Console to monitor air pressure within the drivetrain.  Should the needle ever swing past 25 psi when the system is engaged, it's an instant sign that something is amiss...

AIR SEATING

The cab's interior is quite roomy and can seat three with a stock bench seat on the passenger side.  However, since I had plenty of headroom after raising the cab roof, I wanted more comfortable seats then what Mercedes-Benz offered the Bundeswehr.  A good friend of mine drives for a huge trucking/retail company, and they had recently updated their fleet, nationwide.  Due to a screw-up from the manufacturer, the new trucks shipped with the wrong National Seating air seats.  

International agreed to replace all the seats with the correct ones, but did not want to ship all the trucks back for the change-out.  They simply shipped the new seats to the depots, and had the trucking company's mechanics change the seats.  And then GAVE them the seats!  Through my friend, I was able to purchase two $400 OTR truck seats for $50 each!  Here they are, and they are really comfortable...